Carbon-carbon composites (CC composite for short) are extensively used as aircraft brake pad materials on account of their excellent tribological behaviour at high sliding speeds. It is well known that the tribological behaviour of CC composites is dependent on the nature of the fibre lay up, heat treatment condition employed, etc. More importantly, CC composites also exhibit a transition from a low friction coefficient (μ), normal wear regime, to a high μ, dusting wear regime, when the PV value (P is normal pressure and V is sliding velocity) exceeds a critical value. It is also generally accepted that the above transition is associated with the attainment of a critical temperature at the interface between the two CC composite bodies sliding against each other. The objectives of the present work are two-fold. First, to characterize the transition from normal to dusting wear on the basis of accurate measurement of the interface temperature utilizing an eroding thermocouple and to demonstrate that the attainment of a critical interface temperature is a prerequisite for transition from normal to dusting wear. Second, to study the influence of sample geometry on the critical PV value for transition to dusting wear and to rationalize the above result on the basis of the extent of partitioning of heat generated at the sliding interface into the stationary sample. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.